So, how much can strength training improve an individual’s ability to produce more efficient muscular contractions with secondary effects such as improved global motor function, balance and Range of Movement (RoM) through joints? To draw a clearer picture, the following information is presented as a ‘readers digest’ to the basic inner workings of muscle physiology, the musculoskeletal system and the adaptations reported through acute and chronic periods of strength training in both able bodied and Cerebral Palsy (CP) individuals.
Firstly, it is not ground-breaking news that a consistent period of resistance training can play an integral role in developing substantial strength increases. There is a plethora of research spanning many decades supporting the correlation between strength training and strength development (Wilmore and Costill, 2000). Reporting results as high as 25% to 100% improvement within as little as 3-6 months (the key to gain these potential developments are a) the individual b) the volume and intensity of the programme c) the quality of the programme itself, and of course d) the consistency of delivery). However, the burning question; how does an individual produce these results and become substantially stronger? There is a natural assumption that strength gains are directly related to muscle hypertrophy (increase in muscle cross-sectional area), or as it is more commonly referred to, ‘increased muscle tone’. Equally, this works the other way, ‘Atrophy’, also known as (muscle waste) is reported when muscle cross-sectional area decreases, commonly seen when an individual is dormant, restricted through movement or wearing a cast for a number of weeks or months, and indeed, inconsistency of the delivery of the programme. (note, the potential for increased hypertrophy is associated with an individual’s maturation state. Neurological development through increased motor control and skill development can manifest itself in individuals that are pre-pubertal by using strength development also).
As we are aware of the importance of increased muscle size for increased strength potential, we can begin to look at the most effective way to develop the physical quality of strength and its associated benefits. The other important component to consider during this process is the brain and its Neural pathways. These play almost as an important role as muscle size, with studies reporting a change in neural control of the trained muscle during strength training (Wilmore and Costill, 2000). The neural control is part of the motor system that allows an individual to carry out the most basic of tasks (arm flexion) to the more complicated and skillful movements and activities such as crawling, walking, skipping, running and jumping. These are all important developments that form part of a child’s progression. To put it simply, we are not just training a muscle for increased size and strength, but we are developing a more effective motor unit recruitment of the given muscles. This results in a far greater physical function and ability to produce and initiate muscle contractions, allowing for more precise execution and control over the most basic or most skillful of movement patterns, which can often be taken for granted.
Now that the ‘fluffy’ anatomy and physiology is taken care of, lets discuss the impact on strength interventions that have been used in the specific case of an individual who has Cerebral Palsy. The research carried out on 21 diplegic or hemiplegic children with spastic cerebral palsy looked at interventions for muscle function and Achilles tendon mechanical properties using two different protocols; ‘Progressive Resistance’ (PR) or ‘High-Intensity Strength Training’ (HIST) evaluating its adaptations in Achilles tendon and muscle strength of the plantar flexors in children. Results from this study showed the HIST protocol performed 3 times a week for 8 weeks, reported a significant increase of 28% on absolute peak torque and Achilles tendon stress, with the PR protocol reporting increases of 21% respectively – (Kruse et al; 2017). In simple terms, a development of strength and control in the ankle complex.
The important information to identify from this study, is that both protocols may differ in intensity but the interventions themselves are both underpinned by a programme that aims to develop strength using a programmed, systematic and consistent approach. Both protocols reported significant increases in strength from a programme carried out 3 times per week for 8 weeks. Of course, this is an ideal scenario, but the key elements here are the consistency of approach.
A paper by Park et al., 2017 documented a longitudinal study in the form of qualitative research examining results spanning more than twenty years, examining the ‘functional outcomes of childhood Selective Dorsal Rhizotomy (SDR) 20 to 28 years later’. The study reported a multitude of factors, from demographic, emotional, sensory, overall quality of life and increased physical outcomes post SDR. The study included 95 patients aged between two and eighteen years old, with the post-SDR follow up ranging from 20-28 years. Here 79% of patients were reported as having spastic diplegia, 20% spastic quadriplegia and 1% having spastic triplegia. Our examination of this study is not to discuss the outcome of the SDR operation specifically but to identify the results of the post-operative interventions and, or, participation in physical development programmes and their relativity to this procedure.
The results reported 91% of the patients felt that the operation in its entirety benefited them, with only 2% considering it had decreased their quality of life and 88% of the patients reporting they would recommend SDR for future candidates. The information extracted from this study looked more closely at the daily physical activities that continued post SDR, which showed 60% of the participants carrying out muscle strengthening activities at least once a week, with other activities including regularly stretching; Hamstrings – 43%, Heel cords – 36% and playing recreational sports – 22% respectively. Moreover, if only 60% of the participants within this survey actively took part in a strength based programme for a minimum of one time per week, it raises the question; ‘would the percentage of participants who deemed the operation beneficial (91%) have increased if there was a consistent and specific strength training programme in place immediately post SDR?’ It is worthy to note that, follow-up strength development activity duration is varied, and using guidelines for specific strength development (minimum of two sessions per week), perhaps there was scope for further strength progression. Furthermore, a longitudinal strength development programme post SDR may have provided significantly increased results in strength development, and additional qualities such as proprioception, coordination building to gross motor skills (crawling, walking, skipping, running and jumping). In addition, a potential reduction in the requirement for further surgical intervention on the hamstrings, adductors or Achilles tendon lengthening? Further longitudinal research would of course be required to answer such prudent questions.
In Summary – In any rehabilitation programme strength development will always be an underpinning physical quality that is the catalyst and fundamental reason a person will become physically stronger, increased motor control and recruitment of motor units, with an increased potential to develop both fine and gross motor skills, which in turn will provide further development potential coupled with movement efficiency.
It is important is to understand the importance of such development opportunities and the significance of taking part in an appropriate strength training programme that is periodised appropriately, that is focused on short term tangible goals, with empirical evidence of progression, and perhaps most importantly, constantly reviewed based on the individual child and their rate of progression…..hence, an iterative approach is essential for effective development in this very specialised population . The most cliché point I am about to make and many people who know me will hear me say it often… ‘consistency of any training programme is fundamentally key and without this approach you will be lucky to see maintenance of your current physical qualities’, let alone further physical development and you can most certainly forget using the word ‘inconsistent’ and ‘progress’ in the same sentence. Realising that we all live in a realm of reality and understanding that life has a way of throwing many curve balls which can often lead to time constraints, it is pertinent to remind oneself, that making these interventions as consistent as possible and choosing to make it a routine can only be a huge positive and eventually a conditioned attitude to such training will become as routine as brushing one’s teeth in the mornings.
Additional confirmation of the above points is provided in the United Kingdom Strength and Conditioning (UKSCA) Position Statement for Youth Resistance Training (Lloyd, R.S., Faigenbaum, A.D., Myer, G.D., Stone, M.H., Oliver, J.L., Jeffreys, I., Moody, J.A., Brewer, C. and Pierce, K, 2012).
Resistance training (also called strength training) refers to a specialised method of conditioning whereby an individual is working against a wide range of resistive loads in order to enhance health, fitness and performance. Forms of resistance training include the use of body weight, weight machines, free weights (barbells and dumbbells), elastic bands and medicine balls.
Training Volume and Intensity
Volume and intensity are key resistance training variables that are routinely manipulated within a training session, or overall phase of training, depending on the primary training goal of the individual. Volume refers to the total number of times an exercise is performed within a training session, and is comprised of the number of sets, and number of repetitions within each set. Volume can also relate to the overall loading within short- and long-term training blocks, but for the purposes of the current manuscript the former definition will be used. Intensity most commonly refers to the magnitude of resistance that is required to be overcome during a repetition. The relationship between volume and intensity is inverse in nature; the greater the load (intensity), the lower the number of repetitions that can be completed (volume) by the individual. Both variables must be considered synergistically when prescribing resistance training for youth, however, training intensity is arguably more important owing to the injury risk associated with exposing a child or adolescent to excessive external loading at the expense of correct technique.
Training frequency refers to the number of sessions performed within a week. Previous research has indicated that 2-3 sessions per week on non-consecutive days is most appropriate in order to develop muscular strength levels in children and adolescents. Behringer and colleagues recently substantiated these previous recommendations, indicating that across 42 studies (where mean training frequency was 2.7 ± 0.8 sessions per week), training frequency was significantly correlated with increased resistance training effect.
Rhiannon Owens MSc